Filtering device for use in the spinning of synthetic linear polymers



May 14, 1957 w. MUNCH ET AL FILTERING DEVICE FOR usE IN THE SPINNING OF SYNTHETIC LINEAR POLYMERS Filed March 16, 1953 WW mm INVENTOR United States Patent" FILTERING DEVICE FOR USE IN THE SPINNING 0F SYNTHETIC LINEAR POLYMERS Werner Miinch, Cesano Maderno, and Luigi Notarbartolo,

Milan Italy assignors to Perfogit Societa er Azioni Milan: Italy p The invention relates to a filtering device to be employed in the spinning of synthetic linear polymers from the melt.

As it is known, such spinning is efiected by extruding the molten polymer at a controlled rate through a suitable spinning nozzle. It is also known that it is necessary to place a suitable filter ahead of the spinning nozzle. Filters of various types are known such as filters consisting of stacks of nets having an increasing fine mesh towards the spinneret, or consisting of sand layers with a grain size that decreases in the same direction, with the sand being retained above the spinneret by nets.

However the filters hitherto known are not entirely satisfactory. As a matter of fact the purpose of the filtration, as we have been able to determine and as it does not seem to have been well understood until now, is not only that of eliminating any solid impurities, for example carbon-like particles or mechanical impurities which may be present and which might, if they should reach the spinneret, stop up its openings, but also that of retaining gaseous bubbles that may be present and may consist of steam or occluded gases or monomer products or gases formed during the melting by decomposition of the polymer itself. Such bubbles may interrupt the filaments at their exit from the spinneret or at least produce therein cavities or considerable denier variations. Further, if a filter is to be entirely satisfactory, it should not cause an excessive loss of head.

The filters according to the present invention accomplish with complete efiiciency both the above tasks. Essentially, they comprise aseries of metal plates provided with through bores and grooves which, when the plates are juxtaposed define a plurality of narrow capillary channels which force the molten polymer to follow a sufficiently tortuous path in passing through said series of plates and which at the same time retain not only the solid impurities but also the gaseous bubbles, this being due-it is rbelievedto surface tension phenomena.

The metal plates should preferably be made of a material that may be washed each time the filter becomes exhausted whereby it may then be re-used. Since this Washing is conveniently effected by means of nitric acid, in particular when the polymer to be filtered is a polyamide, it is convenient to make the plates of stainless steel, for example nickel-chrome steels. The dimensions of the bores and channels are naturally related to their shapes and to the characteristics of the polymer.

The invention will be better understood with reference to two embodiments to which said invention is not limited and which will be illustrated with the aid of the appended drawings, wherein:

Fig. 1 is a cross-sectional view and partly an elevational view of a filter according to an embodiment;

Fig. 2 is a plan view of an individual plate of the filter shown in Fig. 1; and

Fig. 3 is a cross-sectional view of the plate shown in Fig. 2.

In the first embodiment depicted in Fig. 1, the numeral 10 denotes a casing which serves as a support for the filter to which the polymer is fed from conduit 18 and is provided with an outlet opening 13 for the filtered polymer. Bolts 11 and 12 lock the superimposed plates tightly against ring 19, and opening 13' thereof defines the inlet opening for the polymer to be filtered.

The various plates are indicated by numeral 14, and one of the plates shown in Figs. 2 and 3. The plates are provided .with through bores 15 having a diameter of about 0.20 to 0.5 mm. and about 5 to 7 mm. long. Bores 15 are arranged along several concentric circles, as it is clearly seen in Fig. 2. Corresponding to each circle, there is a preferably semi-circular or like groove 16 which connects the entrances or the exits of all the through bores that are located on the same circle. Since in general the bores 16 of adjacent plates are not in line, the polymer which enters from conduit 18, after having passed through the bores 16 of the first plate, will have to flow along shorter or longer portions of the substantially circular capillary channels 17 defined by the grooves 16 of the lower face of the first plate and the corresponding grooves of the upper face of the second plate. Thereafter the polymer will cross the through bore of the second plate and so on.

In a more perfect embodiment of the invention, the diameters of the through bores are not the same for all plates, but decrease towards the spinneret. For instance, the plate adjacent the spinneret may have 0.20 mm. bores the immediately preceding plate 0.25 mm. bores and so on. The number of the bores depends on the amount of polymer spun in a unit of time. The dimensions of grooves 16 and therefore of channels 17 may also decrease in a like manner towards the spinneret.

It has been found that a filter of this type is perfectly effective for retaining both the impurities and the gaseous bubbles. Another advantage of this filter is that it is made of a material that is a good heat conductor and that may be heated by conduction and that at any rate is excellently adapted to keep the temperature of the polymer and therefore the spinning viscosity at the desired level. This makes it possible to avoid the excessively severe thermal treatments which were necessary to bring the polymer to such a temperature as to cause it to reach the spinneret while still having the required fluidity even after passing through filters made of insulating materials.

We claim:

1. Spinning filter for use in the spinning of synthetic linear polymers from the melt, comprising a casing having an inlet opening for the liquid polymer to be filtered and an outlet opening for the filtered liquid polymer, the centers of said inlet and outlet openings defining a general axis of the filter, a plurality of metal plates having each a cylindrical peripheral surface and two plane parallel opposite faces, said plates being assembled within said casing coaxilly with and perpendicularly to said general axis of the filter and with their parallel opposite faces in juxtaposed contacting relationship, said parallel opposite faces being sufiiciently smooth to effect a seal against the liquid polymer when in contact with one another, said plates being further provided with through bore disposed along concentric circles centered about said general axis of the filter and having circular grooves on their parallel opposite faces, each groove connecting the openings of those of said through bores being disposed on the same one of said concentric circles, and locking means tightly holding said plates within said casing in the aforementioned assembled relationship the through bores of adjacent plates being staggered 3 relatively to each other thereby providing a plurality of staggered paths offlow'from said inlet to said outlet opening of the filter through said through bores and said connecting grooves of said plate.

2. Spinning filter according to claim 1, wherein said through bores and said connecting grooves of said plates define passages for the liquid polymer having a crosssectien that is never substantially less than that of circular passages with a diameter of 0.2 mm. and that decreases as the distance from the inlet opening of the filter increases.

References Cited in the file of this patent UNITED STATES PATENTS 1,262,317 Finney et al. Apr. 9, 1918 Hesselman May 22, 1923 Sperry Jan. 13, 1931 Welch Dec. 4, 1934 Graves Dec. 16, 1941 Hull et al Dec. 16, 1941 Winkler June 2, 1942 Stamsvik Mar. 28, 1944 Goldman Sept. 21, 1948 Sola May 9, 1950 FOREIGN PATENTS Great Britain of 1866 Germany Feb. 28, 1913 France Oct. 2, 1929 Great Britain Jan. 13, 1930 

1. SPINNING FILTER FOR USE IN THE SPINNING OF SYNTHETIC LINEAR POLYMER FROM THE MELT, COMPRISING A CASING HAVING AN INLET OPENING FOR THE FILTRED LIQUID POLYMER, AND AN OUTLET OPENING FOR THE FILTERED LIQUID POLYMER, THE CENTERS OF SAID INLET, AND OUTLET OPENINGS DEFINING A GENERAL AXIS OF THE FILTER, A PLURALITY OF METAL PLATES HAVING EACH OF CYLINDRICAL PERIPHERAL SURFACE AND TWO PLANE PARALLEL OPPOSITE FACES, SAID PLATES BEING ASSEMBLED WITHIN SAID CASING COAXIALLY WITH AND THEIR PARALLEL SAID GENERAL AXIS OF THE FILTER AND WITH THEIR PARALLEL OPPOSITE FACES IN JUXTAPOSED CONTACTING RELATIONSHIP, SAID PARALLEL OPPOSITE FACES BEING SUFFICIENTLY SMOOTH TO EFFECT A SEAL AGAINST THE LIQUID POLYMER WHEN IN CONTACT WITH ONE ANOTHER, SAID PLATES BEING FURTHER PROVIDED WITH THROUGH BORE DISPOSED ALONG CONCENTRIC CIRCLES CENTERED ABOUT SAID GENERAL AXIS OF THE FILTER AND HAVING CIRCULAR GROOVES ON THEIR PARALLEL OPPOSITE FACES, EACH GROVE CONNECTING THE OPENINGS OF THOSE OF SAID THROUGH BORES BEING DISPOSED ON THE SAME ONE OF SAID CONCENTRIC CIRCLES, AND 